The Meter
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
The meter, SI's unit of length, is the distance light travels in a vacuum during a fixed fraction of a second.
Show
Because the defining constant is light's speed, any lab with an accurate clock can reproduce it without a bar.
Watch for
Students often picture the meter as a physical bar in a vault — true until 1960, not today. (NIST/BIPM, Aug 20, 2026.)